It has been conventionally thought that regeneration of the central nervous system does not occur. However, the repent discovery of endogenous neural stem cells in adult brain has pointed out a possibility that nerve regeneration occurs even in a matured brain. For example, constitutive neurogenesis by neural stem cells has been previously shown in the subventricular/olfactory nervous system and the hippocampal dentate gyrus of an adult rat brain. Moreover, it is known that along with brain lesion, neural stem cells appear and proliferate at other sites such as the cerebral neocortex or the striatum, and therapeutic application of these neural stem cells that appeared and proliferated to cerebrospinal damage or neurodegenerative disease etc. is greatly expected (Non-Patent Literatures 1 and 2).
Animal neural stem cells are known to differentiate into nerve cells and glial cells (astrocytes and oligodendrocytes) (multipotency). Moreover, animal neural stem cells can reproduce cells hang the same multipotency by division (self-renewal ability).
Animal neural stem cells can be employed for regenerative medicine (such as transplantation therapy), and can also be employed as an assay tool (such as an assay tool for exploring differentiation control system). Accordingly, animal neural stem cells have gathered a great deal of attention, and various analyses are being performed on animal neural stem cells.
Animal neural stem cells can be cultured by adding a proliferative factor (EGF, FGF) (Non-Patent Literatures 3 and 4). When animal neural stem cells are employed for regenerative medicine or employed as an assay tool, (1) maintenance of the ability to be able to proliferate (“self-propagation ability” or simply “proliferation ability”) or (2) maintenance of the ability to be able to produce nerve cells by differentiation induction (“differentiation potential into a nerve cell”) and the like are essential.
However, neural stem cells are generally known with repeated passaging to (1) have reduced self-propagation ability, as well as (2) lose its differentiation potential into a nerve cell and become more prone to being differentiated into glial cells (Non-Patent Literature 5). Accordingly, a technology for continued passage of neural stem cells for a longer generation while maintaining both “self-propagation ability” and “differentiation potential into a nerve cell” is essential.
A non-human genetically modified animal having the N-type calcium channel gene knocked out is known. It is also known that said animal is employed for screening agents involved in the control of blood pressure, transmission of pain, control of blood glucose level, and the like (Patent Literatures 1 and 2). Inhibition of the function or expression of the N-type calcium channel in neural stem cells with an inhibitor to verify the inhibition state of neural activity is also known (Non-Patent Literature 6).